1. Field of the Invention
The invention relates to a method for the generation of wheel acceleration and wheel deceleration automatic control signals for an anti-lock system including at least one microprocessor, where the anti-lock system monitors the wheel behavior of one or several vehicle wheels.
2. Brief Description of the Background of the Invention Including Prior Art
It is known with vehicles furnished with an anti-lock system to derive logical signals for the respective wheel behavior from the rotation behavior of the wheels. These signals are in most cases generated digitally for the wheel acceleration (+b), the wheel deceleration (-b), and the wheel slippage (.lambda.). The three signals are combined together in a following logic circuit or by way of a program of a computer. The resulting output signals are amplified in final stages and finally fed to solenoid valves which control the brake cylinders of the individual wheels. It is an object of such an anti-lock system, to prevent a locking of the vehicle wheels by automatically controlling a certain wheel slippage of about 25%, and thus to maintain the steerability of the vehicle in case of an emergency braking as well as to shorten the braking distance. Modern anti-lock systems of the kind recited are furnished with at least one microprocessor and calculate the recited signals by way of a program, compare for example British Patent Document GB-A 2,152,714.
A method is known from the German Printed Patent Document DE-A-2,844,279 for determining the recited acceleration and slippage signals from the rotation behavior of the wheels. The wheels are furnished with toothed Sears which are scanned by rotation speed sensors. The period duration, i.e. the time distance of two neighboring teeth, is determined from the output signals of a wheel sensor while counting of pulses during a period. After division of a constant value by the period duration, there results a digital value, which is proportional to the speed. This process is repeated during each period.
The change of the speed values during a preset time period (.DELTA.t), forming a reference time duration between points in time (t.sub.0 and t.sub.1), is investigated for forming the wheel acceleration (+b) and wheel deceleration (-b), respectively. If the wheel speed changes during this time period relative to the reference value by at least a reference value (.DELTA.v), then a (+b) signal or a (-b) signal, respectively, is furnished depending on the sign of the change direction.
The disadvantage of this measurement method includes that in cases where the speed course exhibits a steep drop, and where the derivative of the speed, i.e. the acceleration jumps, then the threshold of the speed change (.DELTA.v) does not have to be reached completely at the point in time (t.sub.1) even though, for a short time, a relatively high change of the speed can have occurred during the time duration (.DELTA.t). In this case, it can occur that a (+b) or (-b) signal is furnished, only when the reference duration .DELTA.t has been passed through two times. This results in nonuniform automatic control amplitudes of the anti-lock device since the pressure decrease and the pressure build-up, respectively, occur with a time delay.
The German Patent DE 2,553,000-C2 to Hans Mueller et al. teaches an anti-lock automatic control system. The output signal of a time member (7) is fed to a monostable multivibrator (26). The monostable multivibrator in turn is connected to the brake pressure control device (22) and the multivibrator controls the brake pressure control device (22) depending on the switching signal such that, in each case, at the start of a period (.DELTA.t), there is initiated a pressure build-up of a time duration (.DELTA.) and that, in each case, in the following phase (.DELTA.t-.DELTA.) the pressure is maintained constant.
The German Printed Patent Document Laid Open DE-OS-3,906,680-A1 to Takashi Watanabe teaches a motor vehicle operating brake device. The device measures corresponding values of acceleration of the vehicle wheels and includes a digital low pass filter for obtaining acceleration values by excluding high frequency noise parts in following values from the momentary accelerations.
The German Printed Patent Document Laid Open DE-OS-3,841,956-A1 to Claus Beyer et al. teaches an anti-lock automatic control system, where the wheel slippage is employed. A reference signal is required where the slope of the reference signal is generated by an auxiliary reference signal. The slope is made dependent by the size of the pressure decrease during a control cycle and, in fact, the slope is decreased with an increasing pressure decrease.
The German Printed Patent Document Laid Open DE-OS 3,840,710-A1 to Haruki Simanuki et al. teaches an anti-lock control system for motor vehicles. The reference teaches that an anti-lock control system for motor vehicles is constructed such that in case the calculated vehicle speed along a reference delay gradient line, which is maintained over a predetermined acceleration successive limit of the calculated vehicle speed relative to the wheel speed for a certain time duration calculated from that point in time where the delay of the calculated vehicle wheel reaches for the first time the precedingly recited reference delay gradient line. After the motor vehicle has been braked, the calculated vehicle speed is modified such that it follows a deceleration gradient line with a gradient, where the gradient is smaller as compared to the reference deceleration gradient, which increases the threshold speed value.
The German Printed Patent Document Laid Open DE-OS 3,543,058 A1 to Hans-Wilhelm Bleckmann et al. teaches a method and switching circuit for the processing of the output signals of a rotation speed sensor. A use signal and a reference signal is generated for preparing the output signal of a rotation speed sensor, which generates an alternating voltage depending on the speed and on the amplitude of the rotation speed. The two signals are compared. Depending on the difference of the signals (11, 12,) a pulse-shaped output signal is furnished with the aid of a comparator (7), which output signal follows dynamically the use signal based on an adapter circuit.
The United Kingdom Patent Application GB 2,221,758-A to Toshio Yahagi et al. teaches an estimating speed of a vehicle equipped with anti-lock brakes. The deceleration of the vehicle is based on a differentiated value of a highest wheel speed of all wheels or, in a vehicle where the drive wheels are rigidly coupled, upon a differentiated value of a highest value of the wheel speed of the driven wheels, and the lowest wheel speed of the drive wheels. A speed estimating means compares the previous speed estimate with the present speed in a comparator and then operates a switch.
The U.S. Pat. No. 4,408,290 to Jun Kubo et al. teaches a method and device for determining the acceleration and/or deceleration of a moving object. An acceleration sensor is employed which acts on variable-frequency pulses of a speed sensor signal for recognizing any variation of the pulse period. The periods of groups are known and variable number pulse groups are measured with reference to a fixed-frequency clock pulse signal. The measurement periods of successive groups of equal numbers of pulses are compared. Where the difference between the pulse group period is zero or less than a predetermined value, the number of pulses in each group is increased in order to increase the total number of clock pulses during the measurement interval.
The U.S. Pat. No. 4,315,213 to Manfred Wolff teaches a method for obtaining an acceleration or deceleration signal from a signal proportional to speed as well as an apparatus for performing the method. The most recently ascertained n changes are stored in memory. If a new change is to be stored in memory, the longest stored change is erased and a deceleration or acceleration signal is formed by adding from the stored n changes, at intervals of (.DELTA.t).